The polymers and processes for preparing the same are distinct from the prior art. While it is known to prepare polymers by reaction of substituted or unsubstituted 2-amino-4,6-dihalo-s-triazines with various diamines in organic solvents, the products obtained have no technical importance on account of their low molecular weight. In Millot et al., Bull. Soc. Chim. Fr. (5-6, Pt. 2) 1380 (1975), a high temperature solution condensation process resulted in polymers having a molecular weight of less than 8,000. Another such example is found in U.S.S.R. Pat. No. 197,163 (1967): poly(hexamethylene melamine) and poly(p-phenylene melamine) were prepared with reduced viscosities of less than 0.2 dl/g/measured in dimethylsulfoxide and conc.sulfuric acid, respectively.
Other methods are described in Audebert et al., Chem. Abstr. 72:121995y (1970); Kutepov et al., Chem. Abstr. 74, 142398n; Kutepov et al., Chem. Abstr. 73:45897w; U.S.S.R. Pat. No. 246,839 (1969); U.S.S.R. Pat. No. 253,352 (1969); and U.S. Pat. No. 4,086,204 (1978). In order to increase the solubility of poly(amino-s-triazine)s to facilitate the solution condensation process, many of these previously reported polymers were designed to be highly substituted on the exocyclic amino groups and have large diamine linking units. Because of this, they also contained low concentrations--much less than 25 wt.%--of melamine structural units, in the polymer backbone. Although no mechanical property data are given, it is well known that physical properties, especially thermal and mechanical properties, are closely related to the molecular weight and/or the polymer structure, improving in general with increasing molecular weight. Methods other than the direct condensation of aminodihalo-s-triazines with diamines also are known. In U.S. Pat. No. 3,308,101, the products are not true thermoplastic materials, and, in R. Audebert, Chem. Abstr. 71:22355n, cyanuric chloride was reacted with tetramethylenediamine followed by piperidine, but gave a product with an inherent viscosity of only 0.15 dl./g. measured at 0.5% in concentrated sulfuric acid. The foregoing patents and publications are incorporated herein by reference.
In contrast with the products of the prior art processes, which have properties which render them of no practical importance as plastics, it has now been discovered that such products can be produced according to the present invention in forms which are essentially linear, high molecular weight, i.e., an inherent viscosity of at least 0.55 dl./g. and with an triamino-s-triazine unit content of at least 25 weight percent.
The novel, high molecular weight, linear poly(alkylenemelamine) resins of the present invention exhibit high tensile and flexural modulus, good burn resistance, high indentation resistance, exceptional surface hardness, and outstanding resistance to organic solvents. They can be molded or extruded into films, fibers, filaments, and other shaped articles. Composites can be prepared using a variety of fillers and reinforcing agents, such as glass filaments, aramide fibers and graphite fibers. The polymers are suitable for specialized uses in a number of engineering-type or electronic applications.